1. Field of the Invention
The present invention relates to an electronic musical instrument which produces a noise-free, good quality musical tone through utilization of what is called a double buffer system for synthesizing successive different musical waveforms. 2. Description of the Prior Art
Heretofore there has been employed a system of the type in which a musical waveform is synthesized by sampling musical waveform data of one cycle at successive sample points and is appended with a corresponding frequency, thereafter being written into a memory in a write time slot and then read out therefrom in a different readout time slot.
With this system it is possible to obtain an electronic musical instrument which employs a memory with a storage capacity of only one cycle and is relatively low-cost.
The prior art system produces a time variant wave whose waveform varies with time. In the case where a new synthesized musical waveform is written into the memory when the immediately preceding synthesized waveform is being read out therefrom, if the former has substantially the same temporal variation as does the latter as depicted in FIG. 8A, that is, if the level difference between the two successive synthesized musical waveforms is small or slight, then no noise will be generated in the resulting musical tone even if the newly written musical waveform is read out at a frequency corresponding thereto.
However, where two successive synthesized musical waveforms greatly differ in their temporal variation as shown in FIG. 8B, that is, where the level difference between them is large, noise will be generated in the musical tone when the newly written musical waveform is read out at the frequency corresponding thereto. Therefore, in the case of synthesizing a musical tone faithful to its original tone, if two successive synthesized waveforms have largely different temporal variations, then an abrupt level change will naturally occur at the attack portion of the resulting musical tone which represents a feature of the original musical tone; and so that it is difficult to faithfully reproduce the musical tone at the attack portion thereof, resulting in a failure to faithfully reproduce the original musical tone.
This defect is attributable to the use of only one waveform memory which is accessed in different time slots for writing thereinto and reading out therefrom successive synthesized waveforms. To obviate the defect of the prior art, the present invention employs two waveform memories which are accessed for write and readout independently of each other so that a synthesized waveform being written into one of them will not be read out when they immediately preceding synthesized waveform is being read out of the other waveform memory.
Furthermore, an interpolation between successive waveforms and an interpolation between successive sample points of each waveform are utilized to complement the capability of a waveform generator. The prior art performs these interpolations, using different circuits. The present invention combines the double buffer system and the interpolation, and performs the both interpolations through use of a common interpolation circuit. This will make the waveform being read out undergo a gentle variation, improving the quality of the resulting musical tone.